(1) Field of the Invention
The invention relates to a vesicular imaging composition and process, and to the imaging element used therein. In particular, it concerns an imaging element containing radiation-sensitive vesiculating agents within an appropriate matrix and with certain speed-increasing agents.
(2) State of the Prior Art
Vesicular imaging materials, such as films, are of considerable importance in information storage and retrieval, such as in microfilming, because of the extremely stable nature of the image. These materials are well known.
The first commercial vesicular matrices, hereinafter referred to as binders, were originally gelatin. Gelatin was replaced with improved binder materials due to the undesired tendency of gelatin to absorb moisture and therefore to cause a loss of image-forming bubbles and the destruction of the image. Typical improved materials included a great variety of synthetic polymers, such as poly(vinyl chloride), poly(vinylidene chloride), and polystyrene; and copolymers obtained by copolymerizing acrylonitrile with vinyl chloride, styrene, vinylidene chlorofluoride, or 1,1-difluoroethylene; by copolymerizing vinyl chloride with methyl acrylate, acrylic acid, diethyl maleate, or vinyl acetate; or by copolymerizing vinylidene chloride with vinyl chloride, vinyl acetate, vinyl alcohol, ethyl acrylate, or acrylonitrile. Examples of the homo- or co-polymerization of vinylidene chloride are described in U.S. Pat. No. 3,032,414, issued to R. James.
To be suitable, a binder must be sparingly permeable, so as to properly form vesicles from the gas released by the light-sensitive vesiculating agent. To assist in the proper formation of such vesicles, nucleating agents, such as stearic acid, have been added to increase the speed of the vesicular element, and in some cases, to decrease the contrast. Examples of such additions are disclosed in U.S. Pat. No. 3,355,295 issued Nov. 28, 1967, and in Research Disclosure, Vol. 127, November 1974, Publication No. 12709. Although stearic acid and wax nucleating agents contribute significantly to the speed of the element, they do have as a drawback a slight opacity.
Other nucleating techniques have been developed, but generally they require additional processing such as by steaming the element in water. Examples are disclosed in Kosar, Light Sensitive Systems, p. 279 (1965) and in Belgian Pat. No. 790,045 dated Feb. 1, 1973.
Patents relating only to the general background of vesicular elements include U.S. Pat. Nos. 3,779,774; 2,699,392; 2,703,756; and 3,149,971.